A number of bodily passages include valves for ensuring that material in the passage moves in generally one direction. For example, in all vertebrates blood is transported away from the heart and throughout the body via arteries and returns to the heart through veins. To allow for optimal transport of the blood, the arteries and veins include valves that keep the blood flowing in generally one direction through them. In the case of veins, to keep blood moving back toward the heart and to reduce blood pressure build-up, the vessels contain various valves within their lumens, which open to permit blood flow toward the heart and close to limit or prevent backflow of blood, i.e. return of blood toward the extremities. In the case of an artery, valves open to permit blood flow away from the heart and close to limit or prevent backflow toward the heart.
Problems can arise when these valves fail to function properly. For instance, venous valves can become incompetent or damaged (e.g. by disease) such that the backflow of blood is not prevented. When this occurs, blood pressure builds up and the veins and their valves become dilated, particularly in the lower extremities. If enough pressure builds, the condition of venous insufficiency may develop. The severity of this condition is substantial, resulting in swelling, extensive pain, deformities and, in the most severe cases, the development of ulcers can occur. If these ulcers become infected, amputation may ultimately be necessary.
Initial treatments for venous insufficiency have included elevation of the legs or the use of compression stockings. If surgery is determined to be necessary, vein stripping is often performed, which involves the removal of the incompetent or damaged vein(s).
The development of artificial and biological valves has also been suggested to return normal pressure to the veins. There are a variety of these valves described in the art, which are generally designed to allow normal flow of blood back to the heart, while restricting retrograde flow.
However, there remains a needs for improved and/or alternative valve devices and methods, such as for modifying blood flow within vessels on at least a temporary basis. In particular, use of known devices poses risks of thrombogenesis, which must be weighed against the therapeutic effects. Devices that reduce the likelihood of thrombogenic stenosis would provide potential treatments for a wider range of patients and indications. The present disclosure is addressed to these needs.